Electric lamp



Jan. 17, 1939. JBER MAN HA 2,144,521

ELECTRIC LAMP Filed Dec. 6, 1957 2 Sheets-Sheet 1 Di I 7 'lnvehtors zJan Bergmans, Hendrik v. oLVeen',

Wilhelmus L. Verve'st,

Their Attorney- Jan. 17, 1939. J. EFiGMANs ET AL 2,144,521 ELECTRIC LAMPFiled Dec. 6, 1937 2 Sheets-Sheet 2.

Inventors: Jan Bergmans', Hendrik v d. Veen Wilhelmus L,.\/eT"ves1";-,

Thel'f Attorney.

object of our invention is Patented Jan. '17, "1939 UNITED STATEELECTRIC LAMP,

Jan Bergmans',

helmus L. Vervest, Elndhoven,

to General Electric Company, a corposlgnors ration of. New York Hendrikvan der Veen. and Wil- Netherlands, as-

App cation December 6, 1937, Serial No. 178,382 In the NetherlandsDecember 18, 1936 '8 Claims.

Our invention relates to electric lamps comprising an electric energytranslation element, such as a filament, sealed within a bulb orenvelope. More particularly, our invention relates to lamps in which aportion of the bulb is provided with a reflecting surface for thepurpose of projecting the light rays from thefilament into a beam oflight. Such a lamp is particularly suitable for recessed lightingsystems wherein a surface or ceiling is illuminated by light sourceswhich are installed in a cove or recess. 5 Heretofore, the lamps whichhave been generally used for recessed lighting systems have consisted ofa bulb having a neck located in the continuation of the longitudinalaxis of the bulb body or bulbous portion of the bulb. When the length ofthe bulb body of such a lamp is particularly large with respect to thediameter of the bulb body, a. recess of rather large dimensions isnecessary in order to permit installation of the lamp, together with itsholder and fitting, within such recess. This is a real disadvantage,preferable that the recess be as small as possible.

. In addiwn', the usual fittings, together with standard lamps, do notprovide a good efiect, since-- the illumination of the surface orceiling is not uniform while the lateral distribution of the light isnot all that. could. be desired.

- One'object of our invention is to provide an electric incandescentlampsuitable for recessed lighting systems which will permit the use ofa lamp recess of minimum dimensional Another to provide an electricincandescent lamp, for ,such systems, which will provide a uniformillumination' of the surface to be lighted. Still another object of ourinvention is to provide an electric incandescent lamp, for recessedlighting systems, of such construction as to permit the use of a minimumnumber of lighting units to provide the desired uniform illumination ofthe surface to be lighted. I

According to the invention, the bulb is shaped .so that the axis of theof more than '75 degrees, and degrees, with the longitudinal axis of thebulb body, thereby permitting the use of a lamp recess of smalldimensions. is provided with a reflecting coating, so that no separatereflector member or-fittlng is necessary. Accordingly, no space isforthe accommodation of such reflectors and fittings. By means of asuitable shaping of the reflecting portion of the lamp bulb, and themounting of the filament in a meridian plane of since it is recessedlightingbulb neck'forms an angle preferably of 90 I A portion of thebulb itself required -in-- the recess I such bulb, the requirements ofuniform nation are completely satisfied.

Further objects and advantages of our invention will appear from thefollowing description,

of species thereof and from the accompanying 5 drawings, in which: IFig. l is a perspective view of a lamp COmPI1S ing our invention; Fig.21s a transverse sectional view taken along the plane V-V of Fig. 1;Fig. 3

is atop or plan view of the lamp shown in Fig. 1; 10

Fig. 4 is a. top or plan view of a modified form of lamp according toour invention; Figs. 5 and 6 are side and top views respectively ofv arecessed lighting system provided with a lamp according to Figs. 1-3;Fig. "7 is atop view of a recessed. l5 lighting system provided with themodified form of lamp shown in Fig. 4; and Figs. 8 and 9 show the polarlight distribution curves for a lamp comprising our invention accordingto the horizontal plane passing through the axis 3-]; of the lamp 20(Fig. 5) and according to'the vertical or meridian plane of symmetry X-Xof the, reflecting portion of the-lamp (Fig. 6), respectively.-

a first-requirement for the illumination of a plane surface, such asthe. ceiling of a hall or 25 room, by means of a recessed illuminatingsystem, the luminous intensity should beas uniform as possible over theentire surface, In order to satisfy this requirement, the candle powerof the light source must be the greatest in the directions 30 in whichthe part of the ceiling to be illuminated is the farthest away from thelight source. To permit the use of a minimum number of lighting units,it is advantageous to let the light distribution in the lateraldirection enclose the largest 35 possible angle. These variousrequirements for the production of uniform illumination are effectivelyfulfilled by a lamp constructed in accordance with our invention anddescribed hereinafter.

Referring to the drawings, the lamp i comprises a filament 2 sealedwithin a glass bulb or envelope 3 and connected to a base 4 secured tosaid bulb. The bulb 8 consists of a bulbous or bulb body portion 5, anda neck portion 6 the axis D-D of 45 which forms an angle a: of more than'75 degrees and preferably of 91) degrees with the longitudinal axisC-Cof th bulbous portion 5, as shown in Fig. l. The sald'bulbous portion 5is ovoid in shape and is formed as a body of rotation, the 50longitudinal axis (2-0 of said bulbous portion constituting the axis ofrotation. The said body of rotation or bulb body 5 is preferably formedso that a cross-section thereof, according to a meridian plane, willconform in contour to two illumiparts of a parabola, i. e., an upperparabola EF (Fig. 2) and a lower parabola F-G, the foci of whichcoincide, at least approximately, with each other, as shown at L. Thelocus of the coinciding foci L is preferably formed by a circle (Fig. 3)

the plane I--I of which is perpendicular to the axis of rotation CC ofthe bulb body portion 5, as shown in Fig. 2. The top and bottom ends orpoles of the body of rotation are rounded off spherically, as indicatedat H-E and G-J in Fig. 2.

The location of the two axes K-L and M-L I of the upper and lowerparabolas, respectively,

depends on the direction and on the spread of the desired beam of light.From experiments it has been found that when a lamp, according to theinvention, is placed -lna recess and. is used erably located in such away as to form an angle W of an order of magnitude of 80 degrees withthe axis of rotation CC of the bulb body 5. The

connection point of the upper and lower parabolas E-F and FG,respectively, is located on the axis M-L of the lower parabola.

The bulb body 5 is partially provided with a reflecting surface orportion 8, as indicated by cross-sectioning in Figs. 1-4. Thisreflecting surface i comprises approximately one-half of the bulb body5, neglecting the small interruption at the point of connection of thebulb body 5 and bulb neck 5. The limiting plane AA (Fig. 3) of thereflecting surface] coincides approximately with the meridian plane ofthe bulb body 5 extending parallel to the axis DD of the bulb neck 5. Asa result, the meridian plane of symmetry XX of the reflecting surface Iextends perpendicularly to said axis D-D of the bulb neck. As shown inFig. 2, the said limiting plane AA of the reflecting surface i, whileextending parallel to the bulb neck axis DD, is preferably located-at aslight angle 1' to the axis of rotation CC of the bulb body portion 5 soas to extend approximately perpendicularly to the axes K-L and lVi-L ofthe upper and lower parabolas E--F and F-G respectively.

It is desirable, in order to obtain a light distribution which isuniform and almost entirely symmetrical, that the refiecting surface 1have no interruptions such as would occur at the point of connection ofthe bulb body portion 5 and the bulb neck 6 in a bulb of conventionalconstruction. Toobviate such ahiatus in the reflecting surface, anindentation 8 (Fig. 3) is provided at the point of connection of thebulb body 5 and the bulb neck 5 and in radial alignment, according tothe bulb neck axis D-D, with such reflecting surface, whereby the hiatusor interruption therein is considerably reduced.

Within the bulb 3 the filament 2 is mounted on a stems in such a way asto lie in a meridian plane which may form at most an angle of 30 degrees(said angle being 15 degrees in Fig. 4) with the meridian plane ofsymmetry X-X ofthe reflecting surface I. The filament 2 is prefmentlies. The end N of the filament is preferably located in the axis ofrotation CC of the bulb body 5, as indicated in Fig. 2.

By-means of a suitable shaping of the bulb body 5 and of the bulb neck6, the stem tube 9 sealed in the neck of the lamp may be of standardconstruction,.similar to that used in standard incandescent lamps.Excellent results are obtained with a. standard single or multiple coilfilament mounted on such a standard stem tube, so that expensiveprojection lamp filaments are unnecessary.

As it is desirable, for manufacturing reasons, to-employ a stem tube andfilament of such standard construction, it is necessary, in order toplace the filament in the proper position with respect to the coincidingfoci L, that the axis D-D of the bulb neck 6 extend perpendicularly tobut slightly offset from the axis of rotation CC of the bulb body 5. Theamount of such offset is indicated at c in Figs. 2 to 4.

While the indentation 8 in the bulb neck 6 is the preferred method ofpreventing the previously referred to interruptions in the reflectingsurface I, a different solution is disclosed in the modification shownin Fig. 4. In this case, the meridian plane of symmetry XX of thereflecting surface I does not extend perpendicularly to the axis DD ofthe bulb neck, as in the previous form of the invention, but insteadforms an angle 1; therewith of 105 degrees. Accordingly, the limitingplane A=A of the reflecting I surface 1 lies closely adjacent theconventional connection point between the bulb body portion 5 and thebulb neck 6, thereby resulting in very little interruption in thereflecting surface. Even though the filament 2 be not positioned exactlyin the meridian plane of symmetry XX of the reflecting surface,excellent results are nevertheless obtained.

Figs. 5-7 are diagrammatic illustrations showing the manner in which alamp I according to our invention may be mounted within a cove orrecessto provide a recessed indirect lighting system for a room or hallway.The lamp I is mounted within a cove fastened to a side wall I adjacentthe ceiling or surface I I to be illuminated. The said cove consists ofa horizontal shelf or ledge i2 provided with an inclined baffle I3 atits outer end .to thereby render the lamp or light source I, mounted insuch cove, invisible. The lamp I is mounted in a socket I carried by abracket'I5 secured to the horizontal ledge I2. As shown in Fig. 6, thesocket It is so fastened to the bracket I5 as to position the axis D-Dof the bulb neck 6 horizontally and parallel to the side wall Ill. Thelamp I is mounted in the socket It in such a manner as to position theaxes K-L and ML (indicated approximately by the line B-B in Figs. 2 and5), of the two parabolas E-F and F-G, at an'angle e of approximately 15degrees with respect to the ceiling I I. This angle may be varied asdesired, de-

the arrow in Fig. 5.

Where the lamp I is of the modified form shown in Fig. 4, the samemust'be mounted in the .cove I 2-I3 so that the axis D-D of the bulbneck 5 forms an angle (1 of approximately 15 degrees with respect to theside wall I0, as shown in Fig. 7. This is necessary in order to positionthe meridian plane of symmetry X-X 0f the reflecting surface Iperpendicular to the side wall has in the case of the lamp shown themeridian plane of in Figs. 1-3.

As a result of the previously described loca-. tion of the filament 2 inthe lamp, and of the peculiar reflecting characteristics of thereflecting surface I, two beams are formed in the previously mentionedmeridian plane of symmetry x-x of such reflecting surface. One of thesebeams, which is formed by the co-action of the upper parabolicreflecting portion E-F, is subaxis K-L of such stantially parallel tothe portion, while the other beam is substantially parallel to the axisM-L of the lower parabola F-G- Since the lamp i is arranged within thecove Ii -i3 with its axis of rotation C-C substantially vertically, asshown in Fig. 5, the

light beam parallel to the axis K-L therefore illuminates those portionsof the ceiling farthest away while the beam parallel to the axisM-Lilluminates those portions located nearer the lamp. The other portionsof the reflecting surface I, i. e., those portions lying at either sideof symmetry XX, provide 'the illumination extending; transversely ofsuch plane. The spherical lower part G--J of the bulb illuminates theportion of the ceiling located directly above the lamp.

As a consequence of the indicated location of the filament! within thebulb 3, whereby the apparent length 'of such filament is smaller withrespect to the upper reflecting portion E-F than for the lower portionF-G, the beam produced by the lower portion will have a greaterdispersion in the lateral direction than the beam formed by the upperportion E-li. This is desirable in order to obtain a uniformillumination of the ceiling, as the ceiling portions illuminated by thelower portion F-G of the reflecting surface are located closer to thelamp i than those portions which are illuminated by the upper portionEli-F. 1

Referring to Fig. d, showing the polarv light distribution curve, in thehorizontal plane passing through the axis B-BiFig. 5), of a lampconstructed according to our invention,-it is apparent that the width bof the beam is of considerable extent, being much greater than that ofthe lamps heretofore employed. As a result, the lighting units can beplaced at a much greater distance apart than before, while stillmaintaining uniform illumination, and therefore, fewer units arerequired. Furthermore, the points removed from the meridianplane of symmetry X- X of the reflecting surface which are illuminated. from thelight source 0, for instance the points P and Q, are illuminated by alarger candle power than the point B. lying vertical or meridian planeof symmetry X-X H of the reflecting portion 8 of the lamp. Referring tothis curve, it is seen that the ceiling from the point S, which is thefarthest removed from the light source 0, to the point T, which liesapproximately above the lightsource 0, is illuminated with a uniformlydecreasing candle power,

thereby satisfying again the above-mentioned requirements for uniformillumination.

As a result of the fact that the axis D-D of the bulb neck 6 forms anangle of more than provided with a reflecting the lamp may beofdifferent types.

I Letters Patent. of

75 degrees and preferably of 90 degrees with the longitudinal axis -43of the bulb body 5, the advantage occurs that the recess may be made ofminimum dimensions. Since the bulb itself is portion, a separatereflector member is-unnecessary, so that no space need be-provided inthe cove or recess i2i3 to accommodate such a reflector member. Thewidth of the recess or cove l2-i3 can be made of small dimensions due tothe special construction of our lamp, which permits the mounting of sucha lamp within the cove in such a manner that the axis D-D of the bulbneck, and consequently of the socket, is (parallel to the side wall-III, or forms an angle of a rather small value therewith, at most 30degrees, in the case of the modified form of lamp shown in Fig. 4. Theresult is that the dimension a of the cove, as indicated in Figs. -7,can be made illumination. 'Even though the said filament be locatedsomewhat 3 asymmetrically with respect to the reflecting surface 'I, nodetrimental influence on the reflecting characteristics results.

It should be understood that a construction in which alight source, suchas a conventional lamp, is placed in'a reflector having a shape similarto that of a lamp according to our inventlon, by means of which it isalso possible to obtain good'results, is also included within the scopeof the invention. Furthermore, the light emitting element or filamentemployed in Thus, in-

stead of anormal single or multiple coil filament,

it is 'possible'to use a discharge tube. -'Although the bulbous portion5 is preferably paraboloidal in shape, other suitable shapes, such asellipsoidal, may be advantageously employed if desired.

What we claim as new and desire to secure by the United States is:

1. An electric lamp comprising a glass envelope having an ovoid bulbousportion and a neck portion, the axis of said neck portion forming anangle of approximately 90 degrees with the longitudinal axis of saidbulbous portion, said bulbous portion being provided with a. reflectingsurface the limiting plane of which coincides approximately with ameridian'plane of said bulbous portion, and a light source within saidbulb posi ianed approximately in the meridian plane of symmetry of saidreflecting surface.

2. An electric lamp comprising a glass envelope having a bulbous portionand a neck portion, said bulbous portion being formed as a body ofrotation the contour of which, according to a meridian plane, issubstantially defined by the curve of two different parabolas the fociof which approximately coincide, said bulbous portion being providedwith a reflecting surface the limit ing plane of which coincidesapproximately with a meridian-plane of said bulbous portion, and a lightsource within said bulb positioned approximately in the meridian planeof symmetry of said reflecting surface.

3. An electric lamp comprising a glass envelope having a bulbous portionand a neck portion, said bulbous portion being formed as a body ofrotation consisting of two different and substantially paraboloidalhalves, the locus of. the foci of which is defined by a circle the planeof which is perpendicular to the axis of rotation of said bulbousportion, said bulbous portion being provided with a reflecting surfacethe limiting plane of which coincides approximately with a meridianplane of said bulbous portion, and a -light source within said bulbpositioned approximately inthe meridian plane of symmetry of saidreflecting surface. V

An electric lamp comprising a glass envelope having a bulbous portionand a neck por tion, said bulbous portion being formed as a body ofrotation the contour of which, according to a meridian plane, issubstantially defined by the curve of twodifierent parabolas the axes ofwhich form a small angle with each other. said bulbous portion beingprovided with a reflecting surface the limiting plane of which coincidesapproximately with a meridian plane of said bulbous portion, and a lightsource within said bulb positioned approximately in the meridian planeof symmetryof said reflecting surface.

5. An electric lamp comprising a glass envelope having a bulbous portionand a neck portion, said bulbous portion being formed as'a body ofrotation the contour of'which, according to a meridian plane, 'issubstantially defined by the curve of two diflerent parabolas the-axesof which form an angle of an order of magnitude of 80 degrees with theaxis of rotation of said bulbous portion, said bulbous portion beingprovided with a reflecting surface the limiting plane of which coincidesapproximately with a meridian plane of .said bulbous portion, and alight source within said bulb positioned approximately in the meridianplaneof symmetry of said reflecting surface.

6. An electric lamp comprising a glass envelope-having a bulbous portionand a neck portion, said bulbous portion being formed as a body ofrotation the contour of which, according to a meridian plane, issubstantially defined by the curve of two diiferent parabolas the fociof 4 which approximately coincide, said bulbous portion being providedwith a reflecting surface the limiting plane of which coincidesapproximately with a meridian plane of said bulbous portion, and asemi-circular filament sealed within said bulb and positionedapproximately in the meridian plane of symmetry of said reflectingsurface with its center of gravity approximately coinciding with thecommon focus of the parabolas defined by that meridian plane in whichsaid filament lies.

7. An electric lamp comprising a glass envelope having an ovoid bulbousportion and a neck portion, said bulbous portion being provided with areflecting surface the limiting plane of which coincides approximatelywith a meridian plane of said bulbous portion which is substantiallyparallel to the axis of said bulb neck, said bulb neck being providedwith an indentation at its point of connection with said bulbous portionand in radial alignment, according to the bulb neck axis, with saidreflecting surface, and a light source within said bulb positionedapproximately in the meridian plane of symmetry of said reflectingsurface.

8. An electric lamp comprising a glass envelope having an ovoid bulbousportion and a neck portion, said bulbous portion being provided with areflecting surface the limiting plane of which coincides approximatelywith a meridian plane of said bulbous portion which forms an angle ofapproximately 15 degrees with the axis of said bulb neck, and a lightsource within said bulb positioned approximately in the meridian planeof symmetry of said reflecting surface.

JAN BERGMANS. I-IENDRJK VAN nan VEEN. wmnnmos L. VERVEST.

